Lubricating oil compositions for automotive engines (e.g. crankcase lubricants) include additives to enhance the performance characteristics of the lubricant which is typically required by the consumer and by engine manufacturers before certifying the use of a particular lubricant in their engine(s). However, concurrent with the desire to enhance performance characteristics of the lubricant, there has been a continued effort to reduce the content of sulphated ash, phosphorus and sulphur in the lubricant due to both environmental concerns and to insure compatibility with pollution control devices (e.g. catalytic converters and particulate traps).
There are many types of lubricating oil composition additives used to enhance engine performance. Whilst a particular additive may exhibit benefits in one aspect of engine performance that same additive may also exhibit detrimental effects in another aspect. Sulphur containing compounds have been considered as alternative and supplemental additive components in lubricants, especially for their anti-oxidancy performance properties, but these sulphur containing compounds have been used with limited and varying degrees of success, primarily due to the sulphur content of such compounds and the introduction of sulphur into the lubricant, their association with copper corrosion and/or lead corrosion (especially copper corrosion), and their poor compatibility with nitrile elastomer seals which are present in modern internal combustion engines and transmissions. Before certifying a lubricant for use in their engine(s), engine manufacturers (often referred to as “OEMs”) require the lubricant passes a number of performance tests, including tests for compatibility with nitrile elastomer seals, copper and lead corrosion tests.
Accordingly, the present invention aims to provide a lubricating oil composition (especially a lubricating oil composition for an automotive internal combustion engine) that includes a sulphur containing additive component, preferably a sulphur containing anti-oxidant additive component, which, in use, exhibits improved compatibility with nitrile elastomer seals, preferably without significantly compromising the anti-oxidancy performance associated with the sulphur containing additive. The present invention also aims to provide a lubricating oil composition that includes a sulphur containing additive compound, preferably a sulphur containing anti-oxidant additive, wherein the lubricating oil composition exhibits improved copper corrosion and/or lead corrosion performance characteristic(s), especially copper corrosion performance characteristics, preferably without significantly compromising the anti-oxidancy performance associated with the sulphur containing additive.